In a method which produces a corresponding ester from a (meth)acrylic acid by the reaction of the acid with an aliphatic alcohol of 1 to 12 carbon atoms, the esterification proceeds in the form of an equilibrious reaction. When a lower aliphatic alcohol of 1 to 3 carbon atoms is selected as an alcohol source, therefore, the reaction is continuously carried out by using a reactor having a strongly acidic cation-exchange resin packed as a catalyst in the form of a fixed bed therein and the resultant reaction product which is equilibrated in composition is distilled to effect separation of the ester and the formed water from the reaction product. The unaltered (meth)acrylic acid is recovered from the residue for reuse. When a higher aliphatic alcohol of 4 to 12 carbon atoms is selected, there is generally adopted a process which uses sulfuric acid, phosphoric acid, benzenesulfonic acid, or other similar acid as a catalyst, promotes the reaction by expelling the formed water from the reaction system with a solvent such as benzene, toluene, or xylene, deprives the reaction product of acid components through neutralization and washing with water, and finally refines the reaction product.
Recently, use of a strongly acidic cation-exchange resin is recommended even when the esterification is carried out with a higher aliphatic alcohol of 4 to 10 carbon atoms. For example, Japanese Patent Laid-Open SHO 51(1976)-65,712 and Japanese Patent Laid-Open SHO 53(1978)-56,611 disclose a method for esterifying acrylic acid with n-butanol in a reaction column having a strongly acidic cation-exchange resin packed in the form of a fixed bed therein. Japanese Patent Publication SHO 46(1971)-3,041 discloses a method which, in a reactor having a strongly acidic cation-exchange resin as a catalyst for esterification packed in the form of a fixed bed therein and connected to the liquid inlet part and the liquid outlet part of a plate tower, carried out the esterification of acrylic acid with butanol under a vacuum, distils the water formed by the reaction through the top of the tower, and separates the butanol and the ester entrained by the formed water.
None of these methods, however, proves to be satisfactory for the purpose of carrying out the esterification on a commercial scale because in the production of an ester, the selectivity of the reaction for the ester is not sufficiently high. To be specific, these methods are found to suffer from the following disadvantages. In the first place, when the reaction is continuously carried out in a reactor which has a strongly acidic cation-exchange resin packed as a catalyst in the form of a fixed bed, persistence of the water formed by the reaction in the reaction system poses a problem. Since the esterification proceeds in an equilibrious state, presence of water in a liquid state within the reaction system inevitably represses the ratio of conversion. The persisting water further enhances the occurrence of secondary products such as dimeric acids and esters thereof, hydroxypropionic acid and esters thereof and consequently degrades the selectivity of the reaction for the corresponding ester. In the second place, in the esterification using a higher alcohol of 4 to 12 carbon atoms as a raw material, the reaction is promoted by using sulfuric acid, phosphoric acid, benzenesulfonic acid, or other similar acid as a catalyst and causing the formed water to be removed from the reaction system with a solvent such as benzene, toluene, or xylene. During the removal of the formed water, the (meth)acrylic acid is liable to be entrained by the removed water. Effective recovery of the entrained (meth)acrylic acid from the distillate is obtained only with difficulty. Virtually always, the entrained (meth)acrylic acid is inevitably discarded. Even during the course of neutralization and washing with water which follows the course of reaction, the ester produced readily undergoes hydrolysis inevitably to lower the yield of the ester aimed at.
A method which uses a strongly acidic cation-exchange resin as a catalyst and causes this catalyst to be fluidized within the reaction solution has been known to the art. To be specific, Japanese Patent Laid-Open SHO 49(1974)-54,326 discloses a method which comprises introducing an inert gas upwardly into a reaction zone from the lower part thereof, causing the suspension of a catalyst in the reaction solution to be fluidized from the lower part to the upper part of the reaction zone, allowing the suspension to be circulated within a return conduit, and returning it to the lower part of the reaction zone. Since this method effects the fluidization of the catalyst by introducing the inert gas into the reaction zone, it requires introduction of a large amount of the inert gas. Paticularly when the reaction is carried out under a vacuum, this method necessitates incorporation of a voluminous device as for vacuumization in the production system and, therefore, proves to be disadvantageous from the economic point of view.
An object of this invention, therefore, is to provide a method for producing a corresponding ester in a high yield from a corresponding (meth)acrylic acid by the reaction of the acid with an aliphatic alcohol of 1 to 12 carbon atoms.
Another object of this invention is to provide a method for producing a corresponding ester in a high yield from a (meth)acrylic acid by the reaction of the acid with a higher aliphatic alcohol of 4 to 12 carbon atoms.